RePosting this... AGAIN... In the game: Fable 2 in the guilds cave you can jump out from the map and fall down to a ''glitch cave'' where you can find a big circle and a text: Delete.
and further in you can also find a book witch you can't pick up. ( the lonly book)

In the game: Fable 3 you can go to Drift wood and swim out a bit on the sea and see ''The Spire'' from Fable 2 and if you go as far as possible and look down you can see a hidden Lionhead studios logo on the bottom of the sea. ( Lionhead is a big part of the making of Both Fable 2 and 3. )

Crysis 3 have a Thor's hammer mjølner easter egg too. it is hidden in the level "safeties off". but unlike the one in Black ops easter egg, you can actually pick it up there and when using the melee button it will shoot lightning at the target. there's more information in this video

I'm not sure if you already did this but in the Elder Scrolls series, M'aiq the Lair is also in Oblivion and Morrowind and he used to lie to the player telling you that theres a place where you can buy horses (not available in Morrowind game) and dragons to ride on.